Numerous changeable displays wherein a sheet is wound between a pair of take-up rollers having parallel axes have been developed. Such displays are commonly employed in transit vehicles and have been proposed for large advertising displays. Despite the obvious advantages of employing such changeable displays for large advertising signs, to my knowledge, no such signs have been commercially used.
In fabricating a large advertising sign employing conventional structure, as is employed in vehicular displays, I found that there was a significant amount of skewing of the sheet between the rollers. The skewing caused the sheet to wrinkle as it was wound about the take-up rollers, and also caused the sheet to twist as it was being wound on the take-up rollers. In analyzing the problem, I realized that the sheet was not being maintained taut between the take-up rollers. Providing an idler roller in association with each take-up roller did not substantially reduce the slack in the sheet. The problem of slack can be appreciated when it is considered that a display frame typically is defined by a rectangle having a height of approximately 3.5 feet between the take-up rollers and a length of approximately 7.5 feet.
It is, accordingly, an object of the present invention to provide a new and improved large, changeable display of the type wherein a sheet is wound on a pair of parallel rollers.
Another object of the invention is to provide a new and improved sheet winding apparatus wherein wrinkling and twisting of a sheet being wound on a take-up roller is substantially eliminated.
A further object of the invention is to provide a new and improved large, changeable advertising display wherein a sheet is wound between a pair of take-up rollers and slack in the sheet between the rollers is substantially eliminated so that the sheet does not have a tendency to wrinkle or twist as it is wound on a take-up roller.